The syndrome of medullary carcinoma of the thyroid, pheochromocytoma and parathyroid gland hyperplasia (Multiple Endocrine Neoplasm Syndrome - Type II) is transmitted as an autosomal dominant trait with an approximate 50% chance of medullary carcinoma in children of an affected parent. Annual screening of family members 3 years of age and older is being performed in a large kindred relying primarily on pentagastrin as a stimulus for calcitonin release. Elevation in calcitonin levels either baseline or with provocation is considered a marker for medullary carcinoma. Family members have been studied on an annual basis using the ambulatory facilities of the Adult (General) and Children's Clinical Research Centers at the Yale-New Haven Medical Center. Pentagastrin infusion, 0.5 mcg/kg, is performed and serum for calcitonin immunoassay obtained before and at 2, 5, 10 and 20 minutes following. Calcitonin is assayed in the laboratory of Dr. Armen H. Tashjian, Harvard School of Dental Medicine. Screening for parathyroid disease is performed simultaneous with the pentagastrin infusion with total and ionized calcium, alkaline phosphatase and immunoreactive parathormone levels. Urinary catecholamines are obtained on 24-hour collections and assayed in the laboratory of Dr. Lewis Landsberg, Beth Israel Hospital, for pre-symptomatic detection of pheochromocytoma. Of 112 family members available in proximity to New Haven, 72 are participating in the study and no abnormalities have been detected unless previously recognized disease existed. Three members of the family, however, studied in Nashville, Tennessee, were found to have a pre-malignant stage of medullary carcinoma and underwent total thyroidectomy. The Detection Program has also been extended to members of three other families residing in the Southern Connecticut area in whom a parent with medullary carcinoma has been diagnosed.